The present invention relates to a support structure having alternative states of high strength or low thermal conductivity and to a connecting strut having such a support structure.
U.S. Pat. No. 3,814,361 describes a support structure, which includes tubular members that are inserted into one another. Outer, mutually abutting tubular members ensuring a relatively high mechanical strength can be separated as a second strut structure by cooling and then only an inner tubular member, as a first strut structure, carries the mechanical load, the first strut structure remaining connected to the second strut structure and ensuring low thermal conductivity due to a small contact surface relative to one of the tubular members. However, the second strut structure is supported slidingly in the first and therefore only a very limited mechanical strength can be ensured and, for example, the risk of tilting cannot be eliminated.
European Published Patent Application No. 0 584 697 describes another support structure. Shaped components produced from a shape memory alloy are used to separate a support path having a high mechanical strength. Either a support path formed by rings is interrupted by the expansion of a bolt and is partly replaced by a holding device in the form of a spring, or an expansion frame, which serves as a second strut structure and which always remains connected to an object serving as a holding device, is opened and is thus separated from a first strut structure that is in the form of a mechanically less stable strut, on the one end of which the expansion frame acts. The second strut structure is arranged in a plane with and next to the first strut structure, as a result of which only limited stability is ensured.
It is therefore an object of the present invention to provide a support structure having improved stability while still retaining a reduction in the thermal conductivity in one of the operating states. In addition, the support structure may be integrated as simply as possible into existing support structures.
The support structure according to the present invention includes at least one shaped component which is produced from a shape memory alloy and which, in a first operating state of the support structure, results in an increase in the strength of the support structure and, in a second operating state, results in a reduction in the thermal conductivity of the support structure. A first strut structure is surrounded by a second strut structure which has a higher mechanical strength in comparison with the first strut structure, the arrangement surrounding the first strut structure increasing the stability of the arrangement. Furthermore, the first strut structure is connected securely, at least at its one end, to the second strut structure so that there is some mutual support. The first strut structure is also connected to a holding device, and the second strut structure is releasably connected to the holding device by the at least one shaped component so that the first strut structure has further support. Due to the separation of the second strut structure from the holding device, the thermal conductivity of the entire support structure may be reduced under the control of the at least one shaped component which may be particularly adapted and optimized for that purpose.
For example, the second strut structure may, at least partially, be in the form of a hollow strut, and the first strut structure may be in the form of a strut, one end of which is secured to one end of the second strut structure and the other end of which is secured inside the second strut structure. Thus, in a simple manner, the first strut structure is surrounded by the second strut structure.
It is, however, not necessary for the second strut structure to be in the form of a closed hollow strut over its entire length. For example, the second strut structure may be widened at the end to which the first strut structure is secured, and it may have openings in its outer surface, as a result of which access to the first strut structure may be provided at that region.
For example, the holding device may be connected to the first strut structure through the openings in the second strut structure, and the first strut structure may be connected by the shaped components to coupling members that engage in the openings and produce a non-positive-locking connection between the second strut structure and the holding device.
The shaped components may be in any suitable form that triggers their shape memory effect when the temperature exceeds or falls below a specific threshold temperature and that thereby permits movement of the coupling members. Thus, the coupling members may be moved from a coupling position into a decoupling position. In particular, the shaped components may be in a form such that, when the temperature exceeds or falls below a threshold temperature, longitudinal expansion of the shaped components occurs, and they cause the coupling members to be lifted from the second strut structure.
The other members of the support structure may likewise be in a suitable form. The first strut structure may have a low thermal conductivity with sufficient mechanical strength, and the second strut structure may have a high mechanical strength. For example, the first strut structure may be in the form of a cable. The shaped components may be in the form of bolts or screws connected to the first strut structure. The coupling members may be constructed as lid-like members, the shape of which may be adapted to the shape of the openings in the second strut structure in order to ensure an effective non-positive-locking connection.
In order to achieve sufficient variability of the support structure despite the given mechanical strength thereof, the holding device may be connected rotatably to the first strut structure and, at least in the first operating state, also rotatably to the second strut structure. The ability to rotate may be provided by a hinge-type articulation in one plane only or by a ball-and-socket-type joint. A high degree of mechanical strength is thus retained.
The foregoing support structure may be used in any suitable application. Due to the provision of a mechanically strong operating state and a thermally low-conducting operating state, applications are appropriate wherever a high mechanical strength is to be ensured in a first stage of an arrangement""s operation, for example, during a transport stage, and a high degree of thermal insulation is to be achieved in a second stage, for example, during a cooling or heating stage. Therefore, the present invention may be used in a connecting strut for connecting structural members having different temperatures.